Removal and/or melting of snow and ice on airport runways is a major task. Moreover, because of the special corrosion problems caused by use of aluminum, aluminum alloys and other special metals on aircraft, conventional deicing compositions used on roadways, such as road salt and calcium chloride are not acceptable. Unacceptable levels of corrosion to these metals, especially to aluminum, could affect the functioning of the mechanical components as well as the structural integrity of the aircraft.
Accordingly, there have been heretofore two primary substances used to deice airport runways, one being a liquid, ethylene glycol, and the other being a solid, urea. Urea is the only solid currently acceptable for use on airport runways. The SAE standards of corrosion applying to airport deicing compositions apply only to liquids (AMS 1426A) or to urea (AMS 1730A). The differences between these two standards are due to the nature of the respective materials, but the corrosion tests are the same in both cases. However, both ethylene glycol and urea have recently been subject to criticism because of their adverse environmental effects. For example, urea may contaminate lakes and streams and is detrimental to fish and other aquatic life.
Therefore, alternative substances for use on airport runways are needed. One potential class of compounds comprises calcium magnesium acetate (abbreviated as CMA) which is made in various forms. For example, the Federal Highway Administration report entitled "Alternative Highway Deicing Chemicals" published March 1980, identified CMA as a leading candidate for replacing road salt. However, CMA fails certain corrosion tests, particularly on aluminum and aluminum alloys, by staining or discoloring the metal surface. Since there is currently no accepted SAE test procedure for measuring corrosion of solids (other than urea) for use on airport runways, we assume that AMS 1730 applies, and one of the tests under that standard is the sandwich corrosion test, test method ASTM F1110-88. We have found that commercially available CMA fails the Sandwich corrosion test by staining or discoloring test coupons.
Therefore, in that the currently acceptable deicing compositions used on airport runways are under severe criticism for their environmental disadvantages and being that conventional solid deicing compositions utilized for roads have unacceptable corrosivity for aluminum and aluminum alloys, there is a need to develop an alternative deicing composition specifically for use on airport runways.
It is therefore an object of the present invention to provide novel deicing compositions which are useful for use on airport runways and which pass the sandwich corrosion test.
It is a further object of the present invention to present methods for preparing such deicing compositions.
It is yet another object of the invention to provide calcium magnesium acetate modified by an organic chelating agent which is a useful deicing composition, while also being non-staining and non-corrosive to aluminum and aluminum alloys.
These and other objects of the invention will be apparent from the following description and from the practice of the invention.